PPS 15: Planning and Flood Risk
Annex A: Groundwater Flooding
A6 Elevated levels of groundwater resulting from prolonged periods of heavy rainfall can cause the flooding of basements and inundation of other underground structures, the ponding of water in low lying areas and the re-emergence of normally dry groundwater springs. Groundwater flooding often happens over and around aquifers where the underlying geology is highly permeable and has a high capacity to receive and store rainfall. It can result in high levels of infiltration of underground services and can increase damage from prolonged damp penetration since once it occurs it will often take a long time for groundwater levels to fall and for flooding to abate. Most significantly, this type of flooding can occur outside flood plains and can be very localised in extent. It is however uncommon in Northern Ireland.